The American Airlines pilot who died Monday on a flight from Phoenix to Boston was a 57-year-old captain who started his career at Tempe-based America West Airlines in 1990.

American Airlines CEO Doug Parker said in a letter to employees Monday night that Capt. Michael Johnston was piloting Flight 550 from Phoenix to Boston early Monday morning when he fell ill. Parker, who previously was America West's CEO, called it "extremely sad news.''

"All of us at American extend our condolences to Mike’s wife, Betty Jean, and to his entire family,'' he said in the letter. "They have lost a husband and father, and many of you have lost a personal friend. Taking care of Mike’s family is our focus now, and I know you’ll join me in keeping them in your thoughts and prayers.''

Parker said Johnston was a graduate of Brigham Young University. He joined America West as a first officer on the Dash-8. He later flew the Boeing 737 and the 757 before being upgraded to captain on the Airbus A320. America West merged with US Airways in 2005. US Airways and American merged in 2013.

Johnston was based in Phoenix but lived in Utah, according to his Facebook profile. A post on his page Monday said his wife wanted everyone to know that "Mike passed away this morning doing what he loved most.''

Parker also praised the other crew members on Flight 550.

"They took extraordinary care of Mike, each other and our customers. We couldn’t be more proud of the teamwork this crew showed during an extremely difficult time,'' he said. "Our airport teams in Syracuse and Boston were also instrumental in assisting our customers, and their handling is also greatly appreciated."

US Airways Flight 550, also known as American flight 550, left Phoenix Sky Harbor International Airport at 11:55 p.m. Sunday for Boston. It was diverted to Syracuse after Johnston fell ill and died. The co-pilot, a first officer for American, landed the plane at 7:13 a.m., American/US Airways spokesman Andrew Christie said. The two airlines still have separate flight operations, though the US Airways name is being retired this month.

There were 147 passengers and a crew of five aboard the Airbus A320. The flight from Syracuse to Boston landed at 12:34 p.m. Boston time.

Television station KUTV in Utah said Johnston’s wife was told her husband likely died of a heart attack. She told the station her husband had a double bypass in 2006 and was required to get a physical every six months to make sure he was healthy enough to fly.

Johnston says her husband was in good health when he left recently to begin flying.

"He has had problems with his heart," Johnston's wife told the station. "He seemed perfectly fine."

Commercial airline pilots age 40 and older have to have their medical certificates renewed every six months, according to the FAA. Johnson’s was last renewed in June, according to FAA documents.

The in-flight death of a pilot is a rare incident — with only seven other cases on commercial or charter airlines since 1994 — but is one of the many emergencies crews are trained to handle.

Ron Carr, a retired American Airlines pilot who is now an assistant professor at Embry-Riddle Aeronautical University in Prescott, remembers simulator training on such incidents when he joined American in the late 1980s. There are various scenarios where a pilot is incapacitated and a medical emergency is declared, forcing the co-pilot to land the plane.

When he read about the American co-pilot's safe landing of the plane in Syracuse, N.Y., where the flight was diverted after the emergency, he saw such training pay off.

"They did exactly what they were supposed to do, i.e. what they were trained to do: fly the airplane,'' Carr said.

USA Today reported that in a recording of a conversation with air traffic control, Flight 550's first officer can be heard calling in the emergency while saying the captain had become "incapacitated."

"Syracuse, American 550, medical emergency, captain is incapacitated, request handling for runway," the co-pilot said, according to a transcript of a radio transmission posted on the website savvystews.com.

The medical emergency involving one of the pilots in the cockpit means the plane is down to a one-pilot operation. Both pilots in the cockpit, whether ranked captain or first officer, are certified by the Federal Aviation Administration to fly the plane

"They're not frequent, but when they do happen it creates a tense situation, a higher workload situation,'' Carr said. "He's (the remaining pilot) going to get real busy, real quick.''

One of the first orders of business: getting some assistance in landing the plane, from another pilot on the flight, pilot support on the ground or flight attendants.

In 2013, an off-duty United Airlines pilot helped the co-pilot of a United Airlines flight from Houston to Seattle when the captain suffered a heart attack, according to a report in the Seattle Times. The plane landed safely in Boise, where the captain was taken to a hospital and later died.

"The idea is to get some help,'' Carr said. "It lessens my workload (as a pilot) so I don't have to be a single pilot operation anymore.''

American sent a replacement crew to fly passengers from Syracuse to Boston. Carr said that's because the reality of their co-worker's death hits the remaining crew when the plane lands.

"That's when the grief and trauma is going to set in,'' he said.

Since 1994, there have been six other in-flight pilot deaths on commercial airlines and one on a charter carrier, according to FAA spokesman Ian Gregor.